Signal pre-equalizer for fluorescent antennas in optical wireless communications

Fluorescent antennas or fluorescent concentrators enable wide field-of-view (FOV) optical concentration in optical wireless communication systems but introduce bandwidth limitations because of the finite photoluminescence (PL) lifetime of the fluorophores. It has been shown that the frequency response of fluorescent antennas can often be approximated by a single-pole low-pass filter. In this paper, we propose a zero-pole signal pre-equalizer that introduces a zero to cancel the pole introduced by the fluorescent antenna and a new pole at a higher frequency to extend the system bandwidth. In this work, we characterized the frequency response of a fluorescent antenna fabricated in a capillary structure using an organic fluorophore. Our measurement results show that the antenna had a single-exponential PL decay with a lifetime of 5.8 ns and a single-pole frequency response with a 3-dB bandwidth of 27 MHz. Based on this response, bridged-T-based zero-pole pre-equalizers with pole ratios ranging from 1.5 to 3.5 were designed and experimentally validated. In an optical wireless communication system operating at data rates up to 500 Mbps, our measurement results show that pre-equalization consistently reduced the bit error rate (BER) across different transmission data rates and various illumination levels.